arXiv subjects

F. Bufano

Publications and source records attributed to F. Bufano.

At least 91 records · Page 5Linked to original sources

arXiv2013

Comparison of progenitor mass estimates for the type IIP SN 2012A

We present the one-year long observing campaign of SN 2012A which exploded in the nearby (9.8 Mpc) irregular galaxy NGC 3239. The photometric evolution is that of a normal type IIP supernova. The absolute maximum magnitude, with MB = -16.23 +- 0.16 mag. SN2012A reached a peak luminosity of about 2X10**42 erg/s, which is brighter than those of other SNe with a similar 56Ni mass. The latter was estimated from the luminosity in the exponential tail of the light curve and found to be M(56Ni) = 0.011 +-0.004 Msun. The spectral evolution of SN 2012A is also typical of SN IIP, from the early spectra dominated by a blue continuum and very broad (~10**4 km/s) Balmer lines, to the late-photospheric spectra characterized by prominent P-Cygni features of metal lines (Fe II, Sc II, Ba II, Ti II, Ca II, Na ID). The photospheric velocity is moderately low, ~3X10**3 km/s at 50 days, for the low optical depth metal lines. The nebular spectrum obtained 394 days after the shock breakout shows the typical features of SNe IIP and the strength of the [O I] doublet suggests a progenitor of intermediate mass, similar to SN 2004et (~15 Msun). A candidate progenitor for SN 2012A has been identified in deep, pre-explosion K'-band Gemini North (NIRI) images, and found to be consistent with a star with a bolometric magnitude -7.08+-0.36 (log L/Lsun = 4.73 +- 0.14$ dex). The magnitude of the recovered progenitor in archival images points toward a moderate-mass 10.5 (-2/+4.5) Msun star as the precursor of SN 2012A. The explosion parameters and progenitor mass were also estimated by means of a hydrodynamical model, fitting the bolometric light curve, the velocity and the temperature evolution. We found a best fit for a kinetic energy of 0.48 foe, an initial radius of 1.8X10**13 cm and ejecta mass of 12.5 Msun.

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arXiv2013

Moderately Luminous type II Supernovae

Core-collapse Supernovae (CC-SNe) descend from progenitors more massive than about 8 Msun. Because of the young age of the progenitors, the ejecta may eventually interact with the circumstellar medium (CSM) via highly energetic processes detectable in the radio, X-ray, ultraviolet (UV) and, sometimes, in the optical domains. In this paper we present ultraviolet, optical and near infrared observations of five type II SNe, namely SNe 2009dd, 2007pk, 2010aj, 1995ad, and 1996W. Together with few other SNe they form a group of moderately luminous type II events. We collected photometry and spectroscopy with several telescopes in order to construct well-sampled light curves and spectral evolutions from the photospheric to the nebular phases. Both photometry and spectroscopy indicate a degree of heterogeneity in this sample. The light curves have luminous peak magnitudes ($-16.95<M_{B}<-18.70$). The ejected masses of ^56\ni for three SNe span a wide range of values ($2.8\times10^{-2}$Msun$<$M(\ni)$<1.4\times10^{-1}$Msun), while for a fourth (SN2010aj) we could determine a stringent upper limit ($7\times10^{-3}$Msun). Clues of interaction, such as the presence of high velocity (HV) features of the Balmer lines, are visible in the photospheric spectra of SNe 2009dd and 1996W. For SN2007pk we observe a spectral transition from a type IIn to a standard type II SN. Modelling the observations of SNe 2009dd, 2010aj and 1995ad with radiation hydrodynamics codes, we infer kinetic plus thermal energies of about 0.2-0.5 foe, initial radii of 2-5$\times10^{13}$ cm and ejected masses of $\sim$5.0-9.5 Msun. These values suggest moderate-mass, super-asymptotic giant branch (SAGB) or red super-giants (RSG) stars as SN precursors, in analogy with other luminous type IIP SNe 2007od and 2009bw.

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arXiv2013

Spectroscopic Observations of SN 2012fr: A Luminous Normal Type Ia Supernova with Early High Velocity Features and Late Velocity Plateau

We present 65 optical spectra of the Type Ia supernova SN 2012fr, of which 33 were obtained before maximum light. At early times SN 2012fr shows clear evidence of a high-velocity feature (HVF) in the Si II 6355 line which can be cleanly decoupled from the lower velocity "photospheric" component. This Si II 6355 HVF fades by phase -5; subsequently, the photospheric component exhibits a very narrow velocity width and remains at a nearly constant velocity of v~12,000 km/s until at least 5 weeks after maximum brightness. The Ca II infrared (IR) triplet exhibits similar evidence for both a photospheric component at v~12,000 km/s with narrow line width and long velocity plateau, as well as a high-velocity component beginning at v~31,000 km/s two weeks before maximum. SN 2012fr resides on the border between the "shallow silicon" and "core-normal" subclasses in the Branch et al. (2009) classification scheme, and on the border between normal and "high-velocity" SNe Ia in the Wang et al. (2009a) system. Though it is a clear member of the "low velocity gradient" (LVG; Benetii et al., 2005) group of SNe Ia and exhibits a very slow light-curve decline, it shows key dissimilarities with the overluminous SN 1991T or SN 1999aa subclasses of SNe Ia. SN 2012fr represents a well-observed SN Ia at the luminous end of the normal SN Ia distribution, and a key transitional event between nominal spectroscopic subclasses of SNe Ia.

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arXiv2013

HAWK-I infrared supernova search in starburst galaxies

The use of SN rates to probe explosion scenarios and to trace the cosmic star formation history received a boost from a number of synoptic surveys. There has been a recent claim of a mismatch by a factor of two between star formation and core collapse SN rates, and different explanations have been proposed for this discrepancy.} We attempted an independent test of the relation between star formation and supernova rates in the extreme environment of starburst galaxies, where both star formation and extinction are extremely high. To this aim we conducted an infrared supernova search in a sample of local starburts galaxies. The rational to search in the infrared is to reduce the bias due to extinction, which is one of the putative reasons for the observed discrepancy between star formation and supernova rates. To evaluate the outcome of the search we developed a MonteCarlo simulation tool that is used to predict the number and properties of the expected supernovae based on the search characteristics and the current understanding of starburst galaxies and supernovae. During the search we discovered 6 supernovae (4 with spectroscopic classification) which is in excellent agreement with the prediction of the MonteCarlo simulation tool that is, on average, $5.3\pm2.3$ events. The number of supernovae detected in starburst galaxies is consistent with that predicted from their high star formation rate when we recognize that a major fraction ($\sim 60%$) of the events remains hidden in the unaccessible, high density nuclear regions because of a combination of reduced search efficiency and high extinction.

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arXiv2013

Multi-Wavelength Observations of Supernova 2011ei: Time-Dependent Classification of Type IIb and Ib Supernovae and Implications for their Progenitors

We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within 1 day of explosion and span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly and are replaced by Type Ib-like He-rich features on the timescale of one week. High-cadence monitoring of this transition suggests that absorption attributable to a high velocity (> 12,000 km/s) H-rich shell is not rare in Type Ib events. Radio observations imply a shock velocity of v = 0.13c and a progenitor star mass-loss rate of 1.4 x 10^{-5} Msun yr^{-1} (assuming wind velocity v_w=10^3 km/s). This is consistent with independent constraints from deep X-ray observations with Swift-XRT and Chandra. Overall, the multi-wavelength properties of SN 2011ei are consistent with the explosion of a lower-mass (3-4 Msun), compact (R* <= 1x10^{11} cm), He core star. The star retained a thin hydrogen envelope at the time of explosion, and was embedded in an inhomogeneous circumstellar wind suggestive of modest episodic mass-loss. We conclude that SN 2011ei's rapid spectral metamorphosis is indicative of time-dependent classifications that bias estimates of explosion rates for Type IIb and Ib objects, and that important information about a progenitor star's evolutionary state and mass-loss immediately prior to SN explosion can be inferred from timely multi-wavelength observations.

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arXiv2013

Interacting Supernovae and Supernova Impostors. SN 2009ip, is this the end?

We report the results of a 3 year-long dedicated monitoring campaign of a restless Luminous Blue Variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper we present the full historical data set from 2009-2012 with multi-wavelength dense coverage of the two high luminosity events between August - September 2012. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting ~50 days) with a peak of 3x10^41 erg/s, and the 2012b event (14 day rise time, still ongoing) with a peak of 8x10^42 erg/s. The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (~13000 km/s) in September 2011, one year before the current SN-like event. This implies that the detection of such high velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.

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arXiv2012

The Optical SN 2012bz Associated with the Long GRB 120422A

The association of Type Ic SNe with long-duration GRBs is well established. We endeavor, through accurate ground-based observational campaigns, to characterize these SNe at increasingly high redshifts. We obtained a series of optical photometric and spectroscopic observations of the Type Ic SN2012bz associated with the Swift long-duration GRB120422A (z=0.283) using the 3.6-m TNG and the 8.2-m VLT telescopes. The peak times of the light curves of SN2012bz in various optical filters differ, with the B-band and i'-band light curves reaching maximum at ~9 and ~23 rest-frame days, respectively. The bolometric light curve has been derived from individual bands photometric measurements, but no correction for the unknown contribution in the near-infrared (probably around 10-15%) has been applied. Therefore, the present light curve should be considered as a lower limit to the actual UV-optical-IR bolometric light curve. This pseudo-bolometric curve reaches its maximum (Mbol = -18.56 +/- 0.06) at 13 +/- 1 rest-frame days; it is similar in shape and luminosity to the bolometric light curves of the SNe associated with z<0.2 GRBs and more luminous than those of SNe associated with XRFs. A comparison with the model generated for the bolometric light curve of SN2003dh suggests that SN2012bz produced only about 15% less 56Ni than SN2003dh, about 0.35 Msol. Similarly the VLT spectra of SN2012bz, after correction for Galactic extinction and for the contribution of the host galaxy, suggest comparable explosion parameters with those observed in SN2003dh (EK~3.5 x 10^52 erg, Mej~7 Msol) and a similar progenitor mass (~25-40 Msol). GRB120422A is consistent with the Epeak-Eiso and the EX,iso-Egamma,iso-E_peak relations. GRB120422A/SN2012bz shows the GRB-SN connection at the highest redshift so far accurately monitored both photometrically and spectroscopically.

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arXiv2012

SN 2009kn - the twin of the Type IIn supernova 1994W

We present an optical and near-infrared photometric and spectroscopic study of supernova (SN) 2009kn spanning ~1.5 yr from the discovery. The optical spectra are dominated by the narrow (full width at half-maximum ~1000 km s^-1) Balmer lines distinctive of a Type IIn SN with P Cygni profiles. Contrarily, the photometric evolution resembles more that of a Type IIP SN with a large drop in luminosity at the end of the plateau phase. These characteristics are similar to those of SN 1994W, whose nature has been explained with two different models with different approaches. The well-sampled data set on SN 2009kn offers the possibility to test these models, in the case of both SN 2009kn and SN 1994W. We associate the narrow P Cygni lines with a swept-up shell composed of circumstellar matter and SN ejecta. The broad emission line wings, seen during the plateau phase, arise from internal electron scattering in this shell. The slope of the light curve after the post-plateau drop is fairly consistent with that expected from the radioactive decay of 56Co, suggesting an SN origin for SN 2009kn. Assuming radioactivity to be the main source powering the light curve of SN 2009kn in the tail phase, we infer an upper limit for 56Ni mass of 0.023 M_sun. This is significantly higher than that estimated for SN 1994W, which also showed a much steeper decline of the light curve after the post-plateau drop. We also observe late-time near-infrared emission which most likely arises from newly formed dust produced by SN 2009kn. As with SN 1994W, no broad lines are observed in the spectra of SN 2009kn, not even in the late-time tail phase.

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arXiv2012

The bright Type IIP SN 2009bw, showing signs of interaction

We present photometry and spectroscopy of the type IIP supernova 2009bw in UGC 2890 from few days after the outburst to 241 days. The light curve of SN 2009bw during the photospheric phase is similar to that of normal SNe IIP but with brighter peak and plateau (Mmax R = -17.82 mag, Mplateau R = -17.37 mag). The luminosity drop from the photospheric to the nebular phase is one of the fastest ever observed, ~2.2 mag in about 13 days. The radioactive tail of the bolometric light curve indicates that the amount of ejected 56 Ni is \approx 0.022 M\odot. The photospheric spectra reveal high velocity lines of Hα and Hβ until about 105 days after the shock breakout, suggesting a possible early interaction between the SN ejecta and pre-existent circumstellar material, and the presence of CNO elements. By modeling the bolometric light curve, ejecta expansion velocity and photospheric temperature, we estimate a total ejected mass of 8-12M\odot, a kinetic energy of ~0.3 foe and an initial radius of ~ 3.6 - 7 \times 10^13 cm.

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arXiv2011

SN 2009E: a faint clone of SN 1987A

In this paper we investigate the properties of SN 2009E, which exploded in a relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest 1987A-like supernova discovered so far. Spectroscopic observations which started about 2 months after the supernova explosion, highlight significant differences between SN 2009E and the prototypical SN 1987A. Modelling the data of SN 2009E allows us to constrain the explosion parameters and the properties of the progenitor star, and compare the inferred estimates with those available for the similar SNe 1987A and 1998A. The light curve of SN 2009E is less luminous than that of SN 1987A and the other members of this class, and the maximum light curve peak is reached at a slightly later epoch than in SN 1987A. Late-time photometric observations suggest that SN 2009E ejected about 0.04 solar masses of 56Ni, which is the smallest 56Ni mass in our sample of 1987A-like events. Modelling the observations with a radiation hydrodynamics code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an initial radius of ~7 x 10^12 cm and an ejected mass of ~19 solar masses. The photospheric spectra show a number of narrow (v~1800 km/s) metal lines, with unusually strong Ba II lines. The nebular spectrum displays narrow emission lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively strong compared to the [Ca II] doublet. The overall spectroscopic evolution is reminiscent of that of the faint 56Ni-poor type II-plateau supernovae. This suggests that SN 2009E belongs to the low-luminosity, low 56Ni mass, low-energy tail in the distribution of the 1987A-like objects in the same manner as SN 1997D and similar events represent the faint tail in the distribution of physical properties for normal type II-plateau supernovae.

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arXiv2011

SN 2009md: Another faint supernova from a low mass progenitor

We present adaptive optics imaging of the core collapse supernova (SN) 2009md, which we use together with archival \emph{Hubble Space Telescope} data to identify a coincident progenitor candidate. We find the progenitor to have an absolute magnitude of $V = -4.63^{+0.3}_{-0.4}$ mag and a colour of $V-I = 2.29^{+0.25}_{-0.39}$ mag, corresponding to a progenitor luminosity of log $L$/L$_{\odot}$ $\sim4.54\pm0.19$ dex. Using the stellar evolution code STARS, we find this to be consistent with a red supergiant progenitor with $M = 8.5_{-1.5}^{+6.5}$ M$_{\odot}$. The photometric and spectroscopic evolution of SN 2009md is similar to that of the class of sub-luminous Type IIP SNe; in this paper we compare the evolution of SN 2009md primarily to that of the sub-luminous SN 2005cs. We estimate the mass of $^{56}$Ni ejected in the explosion to be $(5.4\pm1.3) \times 10^{-3}$ M$_{\odot}$\ from the luminosity on the radioactive tail, which is in agreement with the low $^{56}$Ni masses estimated for other sub-luminous Type IIP SNe. From the lightcurve and spectra, we show the SN explosion had a lower energy and ejecta mass than the normal Type IIP SN 1999em. We discuss problems with stellar evolutionary models, and the discrepancy between low observed progenitor luminosities (log $L$/L$_{\odot}$ $\sim4.3-5$ dex) and model luminosities after the second-dredge-up for stars in this mass range, and consider an enhanced carbon burning rate as a possible solution. In conclusion, SN 2009md is a faint SN arising from the collapse of a progenitor close to the lower mass limit for core-collapse. This is now the third discovery of a low mass progenitor star producing a low energy explosion and low $^{56}$Ni ejected mass, which indicates that such events arise from the lowest end of the mass range that produces a core-collapse supernova (7-8 M$_{\odot}$).

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arXiv2011

SN 2009jf: a slow-evolving stripped-envelope core-collapse supernova

We present an extensive set of photometric and spectroscopic data for SN 2009jf, a nearby Type Ib supernova, spanning from ~20 days before B-band maximum to one year after maximum. We show that SN 2009jf is a slow evolving and energetic stripped-envelope SN and is likely from a massive progenitor (25-30 solar masses). The large progenitor's mass allows us to explain the complete hydrogen plus helium stripping without invoking the presence of a binary companion. The supernova occurred close to a young cluster, in a crowded environment with ongoing star-formation. The specroscopic similarity with the He-poor Type Ic SN 2007gr suggests a common progenitor for some supernovae Ib and Ic. The nebular spectra of SN 2009jf are consistent with an asymmetric explosion, with an off-center dense core. We also find evidence that He-rich Ib supernovae have a rise time longer than other stripped-envelope supernovae, however confirmation of this result and further observations are needed.

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arXiv2011

The Yellow Supergiant Progenitor of the Type II Supernova 2011dh in M51

We present the detection of the progenitor of the Type II SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini NIRI+ALTAIR, the position of the SN in the pre-explosion images was determined to within 23mas. The progenitor object was found to be consistent with a F8 supergiant star (log L/L_{\odot}=4.92+/-0.20 and T_{eff}=6000+/-280K). Through comparison with stellar evolution tracks, this corresponds to a single star at the end of core C-burning with an initial mass of M_{ZAMS}=13+/-3M_{\odot}. The possibility of the progenitor source being a cluster is rejected, on the basis of: 1) the source is not spatially extended; 2) the absence of excess Hα\, emission; and 3) the poor fit to synthetic cluster SEDs. It is unclear if a binary companion is contributing to the observed SED, although given the excellent correspondence of the observed photometry to a single star SED we suggest the companion does not contribute significantly. Early photometric and spectroscopic observations show fast evolution similar to the transitional Type IIb SN 2008ax, and suggest that a large amount of the progenitor's hydrogen envelope was removed before explosion.

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arXiv2011

The Type IIP SN 2007od in UGC 12846: from a bright maximum to dust formation in the nebular phase

Ultraviolet (UV), optical and near infrared (NIR) observations of the type IIP supernova (SN) 2007od are presented, covering from the maximum light to the late phase, allowing to investigate in detail different physical phenomena in the expanding ejecta. These data turn this object into one of the most peculiar IIP ever studied. The early light curve of SN 2007od is similar to that of a bright IIPs with a short plateau, a bright peak (MV = -18 mag), but a very faint optical light curve at late time. However, with the inclusion of mid infrared (MIR) observations during the radioactive decay we have estimate a M(56Ni) ~ 2\times10^-2 M\odot. Modeling the bolometric light curve, ejecta expansion velocities and black-body temperature, we estimate a total ejected mass was 5 - 7.5 M\odot with a kinetic energy of at least 0.5 \times 10^51 erg. The early spectra reveal a boxy Hα profile and high velocities features of the Balmer series that suggest interaction between the ejecta and a close circum-stellar matter (CSM). SN 2007od may be, therefore, an intermediate case between a Type IIn SN and a typical Type IIP SN. Also late spectra show a clear evidence of CSM and the presence of dust formed inside the ejecta. The episodes of mass loss short before explosion, the bright plateau, along with the relatively small amount of 56Ni and the faint [O I] observed in the nebular spectra are consistent with a super-asympthotic giant branch (super-AGB) progenitor (M~9.7 - 11 M\odot).

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arXiv2011

Studying the SN-GRB connection with X-shooter: The GRB 100316D / SN 2010bh case

During the last ten years, observations of long-duration gamma-ray bursts brought to the conclusion that at least a fraction of them is associated with bright supernovae of type Ib/c. In this talk, after a short review on the previously observed GRB-SN connection cases, we present the recent case of GRB 100316/SN 2010bh. In particular, during the observational campaign of SN 2010bh, a pivotal role was played by VLT/X-shooter, sampling with unique high quality data the spectral energy distribution of the early evolution phases from the UV to the K band.

astro-ph.CO↗

arXiv2011

High luminosity, slow ejecta and persistent carbon lines: SN 2009dc challenges thermonuclear explosion scenarios

SN 2009dc shares similarities with normal Type Ia supernovae, but is clearly overluminous, with a (pseudo-bolometric) peak luminosity of log(L) = 43.47 [erg/s]. Its light curves decline slowly over half a year after maximum light, and the early-time near-IR light curves show secondary maxima, although the minima between the first and second peaks are not very pronounced. Bluer bands exhibit an enhanced fading after ~200 d, which might be caused by dust formation or an unexpectedly early IR catastrophe. The spectra of SN 2009dc are dominated by intermediate-mass elements and unburned material at early times, and by iron-group elements at late phases. Strong C II lines are present until ~2 weeks past maximum, which is unprecedented in thermonuclear SNe. The ejecta velocities are significantly lower than in normal and even subluminous SNe Ia. No signatures of CSM interaction are found in the spectra. Assuming that the light curves are powered by radioactive decay, analytic modelling suggests that SN 2009dc produced ~1.8 solar masses of 56Ni assuming the smallest possible rise time of 22 d. Together with a derived total ejecta mass of ~2.8 solar masses, this confirms that SN 2009dc is a member of the class of possible super-Chandrasekhar-mass SNe Ia similar to SNe 2003fg, 2006gz and 2007if. A study of the hosts of SN 2009dc and other superluminous SNe Ia reveals a tendency of these SNe to explode in low-mass galaxies. A low metallicity of the progenitor may therefore be an important pre-requisite for producing superluminous SNe Ia. We discuss a number of explosion scenarios, ranging from super-Chandrasekhar-mass white-dwarf progenitors over dynamical white-dwarf mergers and Type I 1/2 SNe to a core-collapse origin of the explosion. None of the models seem capable of explaining all properties of SN 2009dc, so that the true nature of this SN and its peers remains nebulous.

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arXiv2011

The He-rich Stripped-Envelope Core-Collapse Supernova 2008ax

Extensive optical and near-infrared (NIR) observations of the type IIb supernova 2008ax are presented, covering the first year after the explosion. The light curve is mostly similar in shape to that of the prototypical type IIb SN 1993J, but shows a slightly faster decline rate at late phases and lacks the prominent narrow early-time peak of SN 1993J. From the bolometric light curve and ejecta expansion velocities, we estimate that about 0.07-0.15 solar masses of 56Ni were produced during the explosion and that the total ejecta mass was between 2 and 5 solar masses, with a kinetic energy of at least 10^51 erg. The spectral evolution of SN 2008ax is similar to that of the type Ib SN 2007Y, exhibiting high-velocity Ca II features at early phases and signs of ejecta-wind interaction from H-alpha observations at late times. NIR spectra show strong He I lines similar to the type Ib SN 1999ex, and a large number of emission features at late times. Particularly interesting are the strong, double-peaked He I lines in late NIR spectra, which - together with double-peaked [O I] emission in late optical spectra - provide clues for asymmetry and large-scale Ni mixing in the ejecta.

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arXiv2010

The Type Ib SN 1999dn: One Year of Photometric and Spectroscopic Monitoring

Extensive optical and near-infrared (NIR) observations of the type Ib supernova 1999dn are presented, covering the first year after explosion. These new data turn this object, already considered a prototypical SNIb, into one of the best observed objects of its class. The light curve of SN 1999dn is mostly similar in shape to that of other SNeIb but with a moderately faint peak M_V=-17.2 mag). From the bolometric light curve and ejecta expansion velocities, we estimate that about 0.11 Msun of 56Ni were produced during the explosion and that the total ejecta mass was 4-6 Msun with a kinetic energy of at least 5x10^{51} erg. The spectra of SN 1999dn at various epochs are similar to those of other Stripped Envelope (SE) SNe showing clear presence of H at early epochs. The high explosion energy and ejected mass, along with the small flux ratio [CaII]/[OI] measured in the nebular spectrum, together with the lack of signatures of dust formation and the relatively high-metallicity environment point toward a single massive progenitor (M_ZAMS>=23-25 Msun) for SN 1999dn.

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